This invention relates to rotary fluid control valves of the butterfly valve type. These valves have a circular fluid flow channel therethrough and a circular disc mounted for rotation between an open position, in which the disc lies substantially parallel to the axis of the fluid flow channel through the valve, and a closed position in which the disc lies perpendicular to this axis. Conventionally, the disc edge contacts a relatively soft or resilient annular seat circumscribing the fluid flow channel when the valve is in the closed position, and the sealing contact between these members will shut off fluid flow through the channel.
Valves of the type just described have not commonly been used in certain applications requiring fire-tested valves. Briefly stated, fire-tested valves are valves that must function as conventional valves in general service, but which must be able to survive exposure to a fire occurring in their environment. Many older, conventional valve types such as gate valves, globe valves and plug valves are metal-to-metal seated, and thus are assumed to be fire resistant. Soft-seated valves, on the other hand, must be certified fire-tested because of several industrial fires several decades ago which were eventually attributed to leakage from rubber or soft-seated valves during a "small" fire, which thus spread out of control when fed by that leakage. Thus, as is apparent, fire-tested valves are often used in flammable fluid service. One of the basic requirements for a fire-tested valve is that there be no loss of performance attributable to the safety feature. Since normally a fire does not occur during the life of the valve, it is expected to function just as a conventional valve would, with equivalent pressure and temperature ratings and cycle life. But, it is also expected to seal within standardized limits after a fire. Several examples of industry standards for fire testing are: American Petroleum Institute (Division of Refining) Standard 607 for Fire Test for Soft Seated Ball Valves; American Petroleum Institute (Division of Production) Standard for Fire Test for API SPEC 6A and 6D Valves; and Oil Companies Materials Association Specification No. FSV. 1, Fire Safe Test for Soft Seat Ball Valves. As is apparent from the titles of those specifications, the most common fire-tested soft seated valves are the ball valve type.
A further desirable feature in butterfly valves is the ability to shut off liquid flow coming from either side of the disc. Many existing butterfly valves are unidirectional, i.e., only one side of the valve may face the upstream side of the flow line if sealing efficiency is to be maintained. It is, of course, desirable for the valve to be capable of shutting off and controlling fluid flow regardless of the direction from which the fluid pressure is applied to the valve.
Still a further desirable feature in butterfly valves is the ability to enhance the sealing effectivenss of the valve by means of the pressure against the seat by the fluid being controlled. Many existing butterfly valves have seat configurations that cannot take advantage of the forces generated by the line pressure when the valve is closed.
It is an object of the present invention to provide a butterfly valve suitable for service with flammable liquids that may be certified as a fire-tested valve, yet provide a simple structure with improved sealing characteristics.
It is another object of the present invention to provide a butterfly valve with the aforementioned fire-tested feature and also to be capable of shutting off and controlling fluid flow regardless of the direction from which fluid pressure is applied to the valve.
It is a further object of the present invention to provide a butterfly valve with a fire-tested feature, an ability to control fluid flow regardless of its direction, and also to enhance the sealing effectivenss of the valve by means of the line pressure, at least as it bears against the resilient seat.
Other objects will become apparent from a consideration of this disclosure.